Cytochemical methods have been used to determine the position of substances in tissues and cells. (1) Two new highly fluorescent tissue-reactive dyes (N-substituted naphthalimides), given the names Lucifer Yellow CH and VS, have been used to mark individual neurons in vivo through recording microelectrodes. (2) Lucifer Yellow CH is being used to examine neurons in inbred and wild populations of the planorbid snail Biomphalaria glabrata in an attempt to study the inheritance of nerve cell shape. BIBLIOGRAPHIC REFERENCE: Feder, N.: Solitary cell and enzyme exchange in tetraparental mice. Nature 263:67-69, 1976.